1. Endocrine System

2. General Functions
Communication
Integration
Control

3. Chemical Messengers
Hormone – substance secreted by an endocrine gland (sometimes from neurosecretory tissues) into the bloodstream that acts on a specific target tissue to produce a given response.

4. Neuroendocrine System
Both the nervous and endocrine system function to maintain stability of the internal environment

5. Names and Locations of Major Endocrine Glands
Hypothalamus
Cranial cavity (brain)
Pituitary gland
Cranial cavity
Pineal gland
Crainal cavity (brain)
Thyroid gland
Neck
Parathyroid glands
Thymus
Mediastinum
Adrenal glands
Abdominal cavity
Pancreatic Islets
Abdominal cavity (pancrease)
Ovaries
Pelvic cavity
Testes
Scrotum
Placenta
Pregnant uterus

6. Classification of Hormones
Classification by function:
Tropic hormones – hormones that target other endocrine glands and stimulate their growth and secretion
Sex hormones – target reproductive tissues
Anabolic hormones
Classification by Chemical Structure
Steroid hormones
Nonsteroid hormones

7. Steroid Hormones
Steroid hormone molecules are made by endocrine cells from cholesterol, an important lipid
All have a characteristic chemical group at the core of each molecule
Lipid-soluble, thus they can easily pass through the phospholipid plasma membrane of target cells.
Examples: cortisol, aldosterone, estrogen, progesterone, and testosterone

8. Steroid Hormone Structure
As these examples show, steroid hormone molecules are very similar in structure to cholesterol (top), from which they are all derived.

9. Nonsteroid Hormones Synthesized mainly from amino acids
Some are proteins (long folded chains of amino acids
Glycoprotein hormones have carbohydrate groups attached to their amino acid chains
Peptide hormones are smaller than protein hormones
Amino acid derivative hormones are derived from a single amino acid molecule

10. Nonsteroid Hormone Structure
A. Protein hormone
Peptide hormone
Amino acid derivative

12. How Hormones Work

13. Hormones signal a cell by binding to specific receptors on or in the target cell. (Like a “lock-and-key”)
Only bind to the receptors
that “fit” them exactly.
Cells can have many different type of receptors
Each hormone-receptor interaction produces different regulatory changes

14. Target Cell Concept

15. Synergism – when hormones work together to enhance each other’s influence on a target cell.
Permissiveness – when a small amount of one hormone allows a second hormone to have its full effect on a target cell.
Antagonism – one hormone produces the opposite effect of another hormone.

16. Mechanisms of Steroid Hormone Action
Can’t travel in plasma because they are lipids
Attach to soluble plasma proteins
Most steroid receptors are found inside cells
Formation of hormone-receptor complex and activates mRNA synthesis

17. Steroid Hormone Mechanism

18. Mechanisms of Nonsteroid Hormone Action
Second messenger hypothesis – theory of hormone action in which the hormone binds to receptors of the target cell, which then triggers a second molecule within the cell to accomplish its function.

19. Example of Second Messenger Mechanism
Hormone-receptor complex
G-protein reacts with GTP
Activation of adenyl cyclases
Phosphates removed from ATP, converting it to cAMP
Activates protein kinase
Activation of specific intracellular enzyme
Enzymes influence specific cellular reactions

20. Regulation of Hormone Secretion
Usually part of a negative feedback loop
Responses that result from the operation of feedback loops within the endocrine system are called endocrine reflexes

21. Calcium-Calmodulin as a 2nd Messenger
1st messenger binds to a receptor in plasma membrane
Activation of membrane bound proteins that trigger the opening of Ca++ channels
Ca++-calmoduln complex formed (2nd messenger)
Activates or inactivates enzyme

22. Endocrine Feedback Loop

23. Prostaglandins (PG’s)
Unique and diverse group that doesn’t meet the usual definition of a hormone.
Rapidly metabolized so
circulating levels are
very low
Produced in a tissue and diffuse a short distance to other cells in the tissue

24. Pituitary Gland Structure
Very small, but very important—sometimes called the “master gland”
Found on the ventral surface of the brain
Actually two glands
Anterior pituitary
Posterior pituitary

25. Structure and Location of the Pituitary Gland

26. Anterior Pituitary (Adenohypophysis)
Composed of several cell types that stain differently from one another
Hormones include:
Growth hormone—growth and blood glucose levels
Prolactin—milk secretion
Tropic hormones—stimulate other glands

27. Growth Hormone Abnormalities

28. Posterior Pituitary (Neurohypophysis)
Storage and release site for two hormones:
Antidiuretic hormone—prevents the formation of large amounts of urine
Oxytocin—stimulates contraction of uterine muscles and causes milk ejection from the breasts (positive feedback mechanisms)

29. Pineal Gland Tiny pine cone shaped structure
Nervous and endocrine system
Functions to support the body’s biological clock
Melatonin—thought to induce sleep

30. Thyroid Gland Located in the neck
Thyroid hormone (TH) – helps to regulate metabolic rate as well as cell growth and differentiation (general target)
Calcitonin – influences tends to decrease blood calcium levels and promote conservation of bone matrix

31. Thyroid and Parathyroid Glands

32. Thyroid Abnormalities

33. Parathyroid Embeded within the thyroid
Secretes Parathyroid Hormone (PTH) – acts as an antagonist to calcitonin by increasing release of calcium into the blood

34. Adrenal Glands Located atop the kidneys Adrenal cortex Adrenal medulla
Aldosterone – sodium homeostasis
Cortisol – many functions
Adrenal medulla
Epinephrine
Norepinephrine

35. Adrenal Gland Structure

36. Pancreatic Islets Edocrine tissue (Islets) account for about
2% or 3% of the total mass of the pancreas
Important pancreatic hormones:
Glucagon – increases blood glucose levels by converting glycogen to glucose
Insulin – promotes movement of glucose out of the blood into the cells

37. Pancreas

38. Regulation of Blood Glucose Levels

39. Gonads
Testes produce androgens (male sex hormones – mainly testosterone which is responsible for male sex characteristics and sperm production
Ovaries
Estrogens – female sex characteristics and reproductive cycle
Progesterone – maintains lining of the uterus for pregnancy

40. Placenta
Interface between the circulatory systems of the mother and developing fetus
Produces human chorionic gonadotropin (hCG) which serves to signal the retention of the uterine lining